cppcheck/man/manual.docbook

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<book>
  <bookinfo>
    <title>Cppcheck</title>

    <date>2009-11-16</date>
  </bookinfo>

  <chapter>
    <title>Introduction</title>

    <para>Cppcheck is an analysis tool for C/C++ code. Unlike C/C++ compilers
    and many other analysis tools, it doesn't detect syntax errors. Cppcheck
    only detects the types of bugs that the compilers normally fail to detect.
    The goal is no false positives.</para>

    <para>Supported platforms:</para>

    <itemizedlist>
      <listitem>
        <para>You can check non-standard code that includes various compiler
        extensions, inline assembly code, etc.</para>
      </listitem>

      <listitem>
        <para>Cppcheck is supposed to be compilable by any C++ compiler that
        handles the latest C++ standard.</para>
      </listitem>

      <listitem>
        <para>Cppcheck is supposed to work on any platform that has sufficient
        cpu and memory.</para>
      </listitem>
    </itemizedlist>
  </chapter>

  <chapter>
    <title>Getting started</title>

    <section>
      <title>First test</title>

      <para>Here is a simple code</para>

      <programlisting>int main()
{
    char a[10];
    a[10] = 0;
    return 0;
}</programlisting>

      <para>If you save that into <filename>file1.c</filename> and
      execute:</para>

      <programlisting>cppcheck file1.c</programlisting>

      <para>The output from cppcheck will then be:</para>

      <programlisting>Checking file1.c...
[file1.c:4]: (error) Array index out of bounds</programlisting>
    </section>

    <section>
      <title>Checking all files in a folder</title>

      <para>Normally a program has many sourcefiles. And you want to check
      them all. Cppcheck can check all sourcefiles in a directory:</para>

      <programlisting>cppcheck path</programlisting>

      <para>If "path" is a folder then cppcheck will check all sourcefiles in
      this folder.</para>

      <programlisting>Checking path/file1.cpp...
1/2 files checked 50% done
Checking path/file2.cpp...
2/2 files checked 100% done</programlisting>
    </section>

    <section>
      <title>Possible errors</title>

      <para>By default, an error is only reported when
      <literal><literal>Cppcheck</literal></literal> is sure there is an
      error. When <literal>--all</literal> is given issues will also be
      reported when <literal>Cppcheck</literal> is unsure.</para>

      <para>The <literal>--all</literal> flag is useful but makes
      <literal>Cppcheck</literal> more unreliable, you will probably get false
      positives.</para>

      <para>Here is a simple code example:</para>

      <programlisting>void f()
{
    Fred *f = new Fred;
}</programlisting>

      <para>Execute this command:</para>

      <programlisting>cppcheck --all file1.cpp</programlisting>

      <para>The output from Cppcheck:</para>

      <programlisting>[file1.cpp:4]: (possible error) Memory leak: fred</programlisting>

      <para>The "possible" means that the reported message may be wrong (if
      Fred has automatic deallocation it is not a memory leak).</para>
    </section>

    <section>
      <title>Stylistic issues</title>

      <para>By default Cppcheck will only check for bugs. There are also a few
      checks for stylistic issues.</para>

      <para>Here is a simple code example:</para>

      <programlisting>void f(int x)
{
    int i;
    if (x == 0)
    {
        i = 0;
    }
}</programlisting>

      <para>To enable stylistic checks, use the --style flag:</para>

      <programlisting>cppcheck --style file1.c</programlisting>

      <para>The reported error is:</para>

      <programlisting>[file3.c:3]: (style) The scope of the variable i can be limited</programlisting>
    </section>

    <section>
      <title>Saving results in file</title>

      <para>Many times you will want to save the results in a file. You can
      use the normal shell redirection for piping error output to a
      file.</para>

      <programlisting>cppcheck file1.c 2&gt; err.txt</programlisting>
    </section>

    <section>
      <title>Unused functions</title>

      <para>This check will try to find unused functions. It is best to use
      this when the whole program is checked, so that all usages is seen by
      cppcheck.</para>

      <programlisting>cppcheck --enable=unusedFunctions path</programlisting>
    </section>

    <section>
      <title>Multithreaded checking</title>

      <para>To use 4 threads to check the files in a folder:</para>

      <programlisting>cppcheck -j 4 path</programlisting>
    </section>
  </chapter>

  <chapter>
    <title>XML output</title>

    <para>Cppcheck can generate the output in XML format.</para>

    <para>Use the --xml flag when you execute cppcheck:</para>

    <programlisting>cppcheck --xml file1.cpp</programlisting>

    <para>The xml format is:</para>

    <programlisting>&lt;?xml version="1.0"?&gt;
&lt;results&gt;
  &lt;error file="file1.cpp" line="123" id="someError" 
               severity="error" msg="some error text"/&gt;
&lt;/results&gt;</programlisting>

    <para>Attributes:</para>

    <variablelist>
      <varlistentry>
        <term>file</term>

        <listitem>
          <para>filename. Both relative and absolute paths are possible</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>line</term>

        <listitem>
          <para>a number</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>id</term>

        <listitem>
          <para>id of error. These are always valid symbolnames.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>severity</term>

        <listitem>
          <para>one of: error / possible error / style / possible style</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>msg</term>

        <listitem>
          <para>the error message</para>
        </listitem>
      </varlistentry>
    </variablelist>
  </chapter>

  <chapter>
    <title>Reformatting the output</title>

    <para>If you want to reformat the output so it looks different you can use
    templates.</para>

    <para>To get Visual Studio compatible output you can use "--template
    vs":</para>

    <programlisting>cppcheck --template vs gui/test.cpp</programlisting>

    <para>This output will look like this:</para>

    <programlisting>Checking gui/test.cpp...
gui/test.cpp(31): error: Memory leak: b
gui/test.cpp(16): error: Mismatching allocation and deallocation: k</programlisting>

    <para>To get gcc compatible output you can use "--template gcc":</para>

    <programlisting>cppcheck --template gcc gui/test.cpp</programlisting>

    <para>The output will look like this:</para>

    <programlisting>Checking gui/test.cpp...
gui/test.cpp:31: error: Memory leak: b
gui/test.cpp:16: error: Mismatching allocation and deallocation: k</programlisting>

    <para>You can write your own pattern (for example a comma-separated
    format):</para>

    <programlisting>cppcheck --template "{file},{line},{severity},{id},{message}" gui/test.cpp</programlisting>

    <para>The output will look like this:</para>

    <programlisting>Checking gui/test.cpp...
gui/test.cpp,31,error,memleak,Memory leak: b
gui/test.cpp,16,error,mismatchAllocDealloc,Mismatching allocation and deallocation: k</programlisting>

    <para></para>
  </chapter>

  <chapter>
    <title>Suppressions</title>

    <para>If you want to filter out certain errors you can suppress these.
    First you need to create a suppressions file. The format is:</para>

    <programlisting>[error id]:[filename]
[error id]:[filename2]
[error id]</programlisting>

    <para>The <literal>error id</literal> is the id that you want to suppress.
    The easiest way to get it is to use the <literal>--xml</literal> command
    line flag. Copy and paste the <literal>id</literal> string from the xml
    output.</para>

    <para>Here is an example:</para>

    <programlisting>memleak:file1.cpp
exceptNew:file1.cpp
uninitvar</programlisting>

    <para>You can then use the suppressions file:</para>

    <programlisting>cppcheck --suppressions suppressions.txt src/</programlisting>

    <para></para>
  </chapter>

  <chapter>
    <title>Leaks</title>

    <para>Looking for memory leaks and resource leaks is a key feature of
    Cppcheck. Cppcheck can detect many common mistakes by default. But through
    some tweaking you can both increase the capabilities and also reduce the
    amount of false positives.</para>

    <section>
      <title>Automatic deallocation</title>

      <para>A common cause of false positives is when there is automatic
      deallocation. Here is an example:</para>

      <programlisting>void Form1::foo()
{
    QPushButton *pb = new QPushButton("OK", this);
}</programlisting>

      <para>Cppcheck can't see where the deallocation is when you have such
      code.</para>

      <para>If you execute:</para>

      <programlisting>cppcheck --all file1.cpp</programlisting>

      <para>The result will be:</para>

      <programlisting>[file1.cpp:4]: (possible error) Memory leak: pb</programlisting>

      <para>The "possible" in the error message means that the message may be
      a false positive.</para>

      <para>To avoid such false positives, create a textfile and write the
      names of the automaticly deallocated classes.</para>

      <programlisting>QLabel
QPushButton</programlisting>

      <para>Then execute cppcheck with the <literal>--auto-dealloc</literal>
      option:</para>

      <programlisting>cppcheck --auto-dealloc qt.lst --all file1.cpp</programlisting>
    </section>

    <section>
      <title>Userdefined allocation/deallocation functions</title>

      <para><literal>Cppcheck</literal> understands many common allocation and
      deallocation functions. But not all.</para>

      <para>Here is example code that might leak memory or resources:</para>

      <para><programlisting>void foo(int x)
{
    void *f = CreateFred();
    if (x == 1)
        return;
    DestroyFred(f);
}</programlisting></para>

      <para>If you analyse that with Cppcheck it won't find any leaks:</para>

      <programlisting>cppcheck --all fred1.cpp</programlisting>

      <para>You can add some custom leaks checking by providing simple
      implementations for the allocation and deallocation functions. Write
      this in a separate file:</para>

      <programlisting>void *CreateFred()
{
    return malloc(100);
}

void DestroyFred(void *p)
{
    free(p);
}</programlisting>

      <para>When Cppcheck see this it understands that CreateFred will return
      allocated memory and that DestroyFred will deallocate memory.</para>

      <para>Now, execute <literal>Cppcheck</literal> this way:</para>

      <programlisting>cppcheck --append=fred.cpp fred1.cpp</programlisting>

      <para>The output from cppcheck is:</para>

      <programlisting>Checking fred1.cpp...
[fred1.cpp:5]: (error) Memory leak: f</programlisting>
    </section>
  </chapter>

  <chapter>
    <title>Exception safety</title>

    <para>Cppcheck has a few checks that ensure that you don't break the basic
    guarantee of exception safety. It doesn't have any checks for the strong
    guarantee yet.</para>

    <para>Example:</para>

    <programlisting>Fred::Fred() : a(new int[20]), b(new int[20])
{
}</programlisting>

    <para>By default cppcheck will not detect any problems in that
    code.</para>

    <para>To enable the exception safety checking you can use
    <literal>--enable</literal>:</para>

    <programlisting>cppcheck --enable=exceptNew,exceptRealloc fred.cpp</programlisting>

    <para>The output will be:</para>

    <programlisting>[fred.cpp:3]: (style) Upon exception there is memory leak: a</programlisting>

    <para>If an exception occurs when <literal>b</literal> is allocated,
    <literal>a</literal> will leak.</para>

    <para>Here is another example:</para>

    <programlisting>int *p;

int a(int sz)
{
    delete [] p;
    if (sz &lt;= 0)
        throw std::runtime_error("size &lt;= 0");
    p = new int[sz];
}</programlisting>

    <para>Check that with Cppcheck:</para>

    <programlisting>cppcheck --enable=exceptNew,exceptRealloc except2.cpp</programlisting>

    <para>The output from Cppcheck is:</para>

    <programlisting>[except2.cpp:7]: (error) Throwing exception in invalid state, p points
at deallocated memory</programlisting>
  </chapter>
</book>